Loads of people having this issue as it's not a very well optimized game. You could try this. Right click on AC3SP then go to properties > compatibility then tick the "Disable display scaling on high DPI settings" box. Should give a bit of a boost to FPS. Minimum specs are 2GB RAM so you should be good. Could lower your screen resolution, and put shadow details on low. Other than that, you need to wait for a patch.
Surface Pro (2017) vs Surface Pro 4